Interfaces (surfaces) that come in contact with air, such as a variety of displays, lenses, show windows, and the like suffer a problem of reduced visibility due to the reflection of solar light, lighting, or the like on their surfaces. As a method for reducing the reflection, a method for laminating several layers of films having different refractive indices so as to match and cancel by interference the reflected light on the film surface and the reflected light at the interface between the film and the base. These films are usually prepared by a method such as sputtering, evaporation, coating, and the like. However, in these methods, there is a limitation on the reduction in the reflectivity and the dependency of the reflectivity on the wavelength even when the number of laminated films is increased. Also, in order to reduce the number of lamination layers to achieve a reduction in the manufacturing cost, there has been a demand for a material having a lower refractive index.
In order to decrease the refractive index of a material, it is effective to use a method of introducing air into the material, for example, a method for forming a fine uneven structure on the surface of a film is widely known. By this method, the refractive index of the whole layers on the surface having a fine uneven structure formed thereon is determined by a volume ratio between the air and the material for forming the fine uneven structure, and as a result, it is possible to remarkably reduce the refractive index, whereby the reflectivity can be reduced even with a small number of lamination layers.
Further, as an antireflective film formed on a glass substrate, there has been proposed an antireflective film in which convex portions having a pyramid shape are continuously formed on the entire film (for example, see Patent Document 1). As described in Patent Document 1, for the antireflective film in which the convex portions having a pyramid shape (fine uneven structure) are formed, the cross-section upon cutting in the film thickness direction continuously changes, and the refractive index gradually increases from the air to the substrate, which thus can be an effective antireflective matters. Also, the antireflective film exhibits excellent optical performances which cannot be reproduced by other methods.
Since the antireflective film with the fine uneven structure as described above is used at an interface in contact with air, it is usually and preferably has imparted thereto an antifouling property and scratch resistance.
As a method for imparting an antifouling property, methods have been proposed for imparting an antifouling property by shedding soiling matter by reducing the surface energy, such as a method in which a coating film including polytetrafluoroethylene is formed on the surface of a fine uneven structure (for example, see Patent Document 2), a method in which a stamper having a fine uneven structure is brought into pressure-contact with a layer formed of a resin composition comprising a fluorine-containing compound (for example, see Patent Document 3), and the like.
Moreover, methods have also been proposed for wiping the attached soiling matter off by floating it on water using surface hydrophilization, such as a method in which a photocatalyst layer (titanium oxide, and the like) having a fine uneven structure is coated on a base surface (for example, see Patent Document 4), a method in which a hydrophilic coating film including inorganic oxides such as a silicic acid compound, and the like is formed on a base surface by sputtering (for example, see Patent Document 5), a method in which an inorganic fine particle solution is spin-coated on the surface of a soda glass and cured by heating (for example, see Patent Document 6), and the like.
As a method for imparting scratch resistance, as in Patent Documents 5 and 6 as above, a method in which inorganic fine particles are dispersed on a coating film or a high hardness resin obtained by curing crosslinkable polyfunctional monomers is generally used.
In addition, without involving a fine uneven structure, a few methods in which a hydrophilic monomer and a polyfunctional monomer are combined to realize the compatibility between the antifouling property and the scratch resistance (for example, see Patent Document 7) have been proposed.
However, the active energy ray-curable resin as described in Patent Document 1 is not hydrophilic, and thus, it has a water contact angle of more than 25°, and as a result, it does not exhibit the antifouling property.
Further, if the surface energy is reduced as described in Patent Documents 2 and 3, little soiling substance adheres, but the soil is caught in the concave portion, and thus, there was a problem that once the soiling substance is embedded, it is hard to remove in use.
In addition, as described in Patent Document 4, in the case of using a photocatalyst, it was difficult for the decomposition of dust to proceed indoors. Also, if a resin film or the like was used as a base and its surface was coated with a photocatalyst layer, there were problems such as the decomposition of even the resin film.
Moreover, with the antifouling article having a fine uneven structure obtained by the preparation method as described in Patent Documents 5 and 6, there were problems in that it was difficult to control the distance between the adjacent convex portions or the height of the convex portion, and that the antireflective property could not be sufficiently obtained.
Furthermore, even though the method as described in Patent Document 7 was applied to a fine uneven structure, there was a problem in that the antifouling property is not sufficiently enforced.
[Patent Document 1] JP-A-63-75702
[Patent Document 2] JP-A-2003-172808
[Patent Document 3] JP-A-2005-97371
[Patent Document 4] JP-A-2001-183506
[Patent Document 5] JP-A-2001-315247
[Patent Document 6] JP-A-11-217560
[Patent Document 7] JP-A-7-316468